The Book Keeper by Sarah Painter

Mysterious, magical, and a little bit deadly… Welcome to Unholy Island.

Luke Taylor was searching for his missing twin brother when he discovered a new purpose on a magical tidal island. Living in a quirky bookshop is a dream come true – he just didn’t expect it to be so damn dangerous.
Running a business on a tiny island was always going to bring challenges, but Luke didn’t bargain on strange customers, hexed books, or a sentient shop that seems to have its own ideas about how things ought to be done.
Not to mention his deepening feelings for the island’s resident witch…
Esme Gray became the island’s Ward Witch seven years ago and has built a life of safety and quiet for herself. A balm for her abusive past.

Her feelings for the new Book Keeper have disturbed those calm waters, and when his life is threatened, she doesn’t hesitate to dive in to help. But is she strong enough to pull them both out alive?